Mithril: Cooperative Row Hammer Protection on Commodity DRAM Leveraging Managed Refresh

Since its public introduction in the mid-2010s, the Row Hammer (RH) phenomenon has drawn significant attention from the research community due to its security implications. Although many RH-protection schemes have been proposed by processor vendors, DRAM manufacturers, and academia, they still have shortcomings. Solutions implemented in the memory controller (MC) pay an increasingly higher cost due to their conservative design for the worst case in terms of the number of DRAM banks and RH threshold to support. Meanwhile, the DRAM-side implementation has a limited time margin for RH protection measures or requires extensive modifications to the standard DRAM interface. Recently, a new command for RH protection has been introduced in the DDR5/LPDDR5 standards, called refresh management (RFM). RFM enables the separation of the tasks for RH protection to both MC and DRAM. It does so by having the former generate an RFM command at a specific activation frequency, and the latter take proper RH protection measures within a given time window. Although promising, no existing study presents and analyzes RFM-based solutions for RH protection. In this paper, we propose Mithril, the first RFM interface-compatible, DRAM-MC cooperative RH protection scheme providing deterministic protection guarantees. Mithril has minimal energy overheads for common use cases without adversarial memory access patterns. We also introduce Mithril+, an extension to provide minimal performance overheads at the expense of a tiny modification to the MC while utilizing an existing DRAM command.